Comment by jwilliams

How many of them need to switch before it become tenuous? -- perhaps if the most profitable go, then it might not be nearly that much.

Google relies on a massive network effect to hold their position - this makes them a very stable system in many regards. However, there is also the risk of a collapse scenario.

In the case of Google, it might only be one or two segments (in whatever demographic/dimension) that are key.